Techniques for tracking a source are known from the field of navigation, radar and sonar. One of the simplest source-tracking techniques employs a crossed dipole array—two dipole sensors centered at the same point and oriented at right angles.
Crossed dipoles have been used for radio direction finding since the early days of radio. S. W. Davies “Bearing Accuracies for Arctan Processing of Crossed Dipole Arrays” in Proc. OCEANS 1987, vol. 19., September 1987, pp 351-356 states that for a crossed dipole array with one dipole orientated towards the north, signals proportional to the sine and cosine of the source bearing are obtained and an estimate of the source bearing, {circumflex over (φ)}, can be obtained through the arctan of the ratio of these components. If there is an additional omnidirectional sensor located at the centre of the crossed dipole array, then its output may be used for synchronous detection of the “sense” or sign of the sine and cosine outputs; this allows the use of a four quadrant inverse tangent function to obtain unambiguous bearing estimates. This article studies the properties of a bearing estimator based on time-averaged products of the omnidirectional sensor uo(t), with north-south oriented (“cosine”) dipole output, uc(t), and east-west oriented (“sine”) dipole output, us(t).
U.S. Pat. No. 6,774,934 relates to camera positioning means used to point a camera to a speaking person in a video conferencing system. In order to find the correct direction for a camera, the system is required to determine the position from which the sound is transmitted. This is done by using at least two microphones receiving the speech signal and measuring the transmission delay between the signals received by the microphones. The delay is determined by first determining the impulse responses (h1) and (h2) and subsequently calculating a cross correlation function between these impulse responses. From the main peak in the cross correlation function, the delay value is determined. The described system is satisfactory when the microphones are spaced sufficiently wide apart that a delay value can be determined.
A drawback of currently known audio tracking techniques is that the dominant reflection of the audio source (via walls and tables for example) negatively influences the result of the audio-tracking.